USB: serial: ftdi_sio: only allow valid latency timer values

Valid latency timer values are between 1 ms and 255 ms in 1 ms steps.
The store function for the "latency_timer" device attribute currently
allows any value, although only the lower 16 bits will be sent to the
device, and the device only stores the lower 8 bits.  The hardware
appears to accept the (invalid) value 0 and treats it the same as 1
(resulting in a latency of 1 ms).

Change the latency_timer_store() function to accept only the values 0 to
255, returning an error -EINVAL for out-of-range values.  Call
kstrtou8() to parse the integer instead of the obsolete
simple_strtoul().

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Johan Hovold <johan@kernel.org>

diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
index 2b9b5119ff1302a4abcc443b5e13b9a0051d0d9e..b774f9d32d4f163dcd84ace836271f931dc90eaa 100644 (file)
--- a/drivers/usb/serial/ftdi_sio.c
+++ b/drivers/usb/serial/ftdi_sio.c
@@ -1716,9 +1716,12 @@ static ssize_t latency_timer_store(struct device *dev,
 {
        struct usb_serial_port *port = to_usb_serial_port(dev);
        struct ftdi_private *priv = usb_get_serial_port_data(port);
-       int v = simple_strtoul(valbuf, NULL, 10);
+       u8 v;
        int rv;
 
+       if (kstrtou8(valbuf, 10, &v))
+               return -EINVAL;
+
        priv->latency = v;
        rv = write_latency_timer(port);
        if (rv < 0)